The structure and operation of wireless communication systems are generally known. Examples of such wireless communication systems include cellular systems and wireless local area networks, among others. In a cellular system, a regulatory body typically licenses a frequency spectrum for a corresponding geographic area (service area) that is used by a licensed system operator to provide wireless service within the service area. A plurality of base stations may be distributed across the service area. Each base station services wireless communications within a respective cell. Each cell may be further subdivided into a plurality of sectors.
Location based services for mobile stations are expected to play an important role in future applications of wireless systems. A wide variety of technologies for locating mobile stations have been developed. Many of these have been targeted towards the Federal Communication Commission's (“FCC”) requirement to determine the location of emergency 9-1-1 callers with a high degree of accuracy. The Wireless Communications and Public Safety Act (“the 911 Act”) was enacted to improve public safety by encouraging and facilitating the prompt deployment of a nationwide, seamless communications structure for emergency services. The 911 Act directs the FCC to make “911” the universal emergency number for all telephone services. Emergency calls from landlines provide the emergency dispatchers with the telephone number and the address of the caller thereby assisting emergency personnel in locating the emergency. As mobile stations became more widely used, an increasing number of emergency calls are being made from mobile stations without a fixed address. Emergency call centers have recognized that relying upon the caller to describe their location caused a delay in service. Many mobile emergency callers were unable to accurately describe their location, resulting in a further delay and, often times, a tragic outcome.
In 1996, the FCC issued a report and order requiring all wireless carriers and mobile phone manufacturers to provide the capability for automatically identifying to emergency dispatchers the location from which a wireless call was made. Implementation was divided into two phases. Phase I required wireless service providers and mobile phone manufacturers to report the telephone number of the mobile phone making the call as well as the base station controlling the mobile station which provided a general area from which the call was made. This information can be obtained from the network elements. Phase II of the FCC's Enhanced 911 (“E-911”) mandate stated that by Oct. 1, 2002, wireless service providers must be able to pinpoint, by latitude and longitude, the location of a subscriber who calls emergency from a mobile station. Wireless service providers were given the option of providing a network-based solution or a handset based solution. Wireless service providers who select a network-based solution are required to locate a mobile phone within 100 meters 67% of the time.
Typical mobile station location technologies may be classified into external methods or network based methods. One example of an external method is the Global Positioning System (“GPS”). Network based methods may be further categorized depending on whether it is the network or the mobile station that performs necessary signal measurements. These signal measurements may involve the reception time of signals communicated between a base station (“BS”) and a mobile station (“MS”), the angle of arriving signals or round trip delay measurements of signals communicated between a serving BS and an MS, or combinations thereof. For example, most location methods require specific hardware in the MS and/or in the network. Traditional networks include Mobile Station Controllers (“MSC”), Base Station Controllers (“BSC”) and Base Transceiver Station (“BTS”) systems that jointly operate to communicate with mobile stations over a wireless communication link.
Examples of common networks include Global System for Mobile Communication (“GSM”) networks, North American Time Division Multiple Access (“TDMA”) networks, Code Division Multiple Access (“CDMA”) networks, Universal Mobile Telecommunications System (“UMTS”) networks, Worldwide Interoperability for Microwave Access (“WiMax”) networks, Orthogonal Frequency Division Multiple Access (“OFDMA”) networks, and WiFi networks. These networks may operate under any one or combination of the following standards: IS-95, Evolution-Data Optimized (“EVDO”), CDMA2000, Long Term Evolution (“LTE”) and 1 times Radio Transmission Technology (“1×RTT”). Extensive infrastructures generally exist in the cellular wireless networks for tracking mobility, distributing subscriber profiles, and authenticating physical devices. In wireless mobile networks providing a facility to determine a mobile station's geographic position, a network component commonly referred to as a Mobile Location Center (“MLC”) performs the location calculation. Furthermore, in some networks, Location Measurement Units (“LMU”) may be generally required for some methods to obtain knowledge about the relative time differences for sending signals to different mobile stations.
A number of applications currently exist within communication systems for which location solutions are needed by mobile units, MSs, user equipment (“UE”), base stations or other devices and by other entities in a wireless network. There exists a need in the art to locate UMTS, OFDMA or W-CDMA mobile devices to satisfy FCC E-911 regulations as well as to provide Location Based Services for mobile phone users and to locate unknown nodes or base stations in a communications system. The 3GPP UMTS standard outlines several methods for location including Cell-ID, A-GPS, Observed Time Difference of Arrival (“OTDOA”), and Uplink Time Difference of Arrival (“U-TDOA”). The standard also provides an overview of the functionality necessary to establish, modify and maintain an UMTS link having a specified Quality of Service (“QoS”). The UMTS radio interface protocol model generally provides control over the multiplexing of traffic flows of different kinds and different origins through a layering of duties.
FIG. 1 is a diagram of a radio interface protocol reference model. With reference to FIG. 1, the radio interface protocol reference model 100 generally includes three layers 10, 20, 30. The first layer (“L1”) 10 is generally a physical layer providing information transfer services as a set of WCDMA transport channels. L1 provides various handover functions, error detection and reporting to higher layers, multiplexing of transport channels, mapping of transport channels to physical channels, fast close loop power control, and frequency and time synchronization, to name a few. The second layer (“L2”) 20 is generally termed as the radio link layer and allows higher layers to see only a set of radio bearers along which different kinds of traffic can be transmitted over the radio link. L2 includes several sublayers including a Medium Access Control (“MAC”) sublayer 22 and a Radio Link Control (“RLC”) sublayer 24. The MAC sublayer 24 generally controls data transfer to the RLC sublayer 24 and higher layers through control of transport block capacity by ensuring that capacity allocation decisions are executed promptly. The RLC sublayer 24 generally adds regular link layer functions onto logical channels provided by the MAC sublayer 22. The third layer (“L3”) 30 is generally termed as the radio network layer. For L3 control protocol purposes the RLC service is generally adequate, however, for domain-specific user data, additional convergence protocols may be needed such as Packet Data Convergence Protocol (“PDCP”) 26 and Broadcast and Multicast Control (“BMC”) protocol 28. L3 includes a Radio Resource Control (“RRC”) sublayer 32 which generally provides the functions of broadcasting information from a network to all UEs, radio resource handling (e.g., code allocation, handover, admission control, and measurement reporting/control), QoS control, UE measurement reporting and control thereof, power control, encryption and integrity protection, to name a few.
The most likely RRC service state when a voice call is active is the Cell_DCH state in which a UE continuously transmits a pilot signal unique within a coverage area. In Cell_DCH, a dedicated physical channel is allocated to the UE in the uplink and downlink spectrums, the UE is known on cell level according to its current active set, and dedicated transport channels, downlink and uplink shared transport channels, or a combination thereof may be utilized by the UE. A reverse pilot channel based location technique is disclosed in co-pending U.S. application Ser. No. 11/008,154, filed Dec. 10, 2004, the entirety of which is incorporated herein by reference. There is, however, a need to implement the location solutions in U.S. application Ser. No. 11/008,154 in a UMTS-based system.
Accordingly, there is a need for a method and system for locating a mobile appliance using an uplink dedicated physical control channel and downlink synchronization channel. Therefore, an embodiment of the present subject matter provides a method for estimating a location of a wireless device in a wireless communication system having a plurality of nodes and a plurality of location measurement units (“LMUs”). Exemplary nodes may be a base station, a sector, a repeater. The method may comprise collecting a plurality of signal samples from a first wireless device and a second wireless device by one or more LMUs in a first search window. A first time of arrival (“TOA”) may be determined from the plural signal samples, and a second search window determined as a function of the first TOA. A second TOA may be determined from the plural signal samples in the second search window. A range estimate of the first wireless device may be determined, and an estimated location of the first wireless device determined as a function of the first TOA, the second TOA, or the range estimate and second TOA.
Another embodiment of the present subject matter provides a method for estimating a location of a wireless device in a wireless communication system having a plurality of nodes and a plurality of LMUs. The method may comprise collecting a set of signal samples from a first wireless device and a second wireless device by one or more LMUs in a search window determined as a function of a first uplink TOA from a first node. A second uplink TOA may be determined at a second node or the one or more LMUs from the set of signal samples. A range estimate of the wireless device may be determined, and estimated location of the wireless device determined as a function of the first uplink TOA, the second uplink TOA, or the range estimate and second TOA.
One embodiment of the present subject matter may provide a method for estimating a location of a wireless device comprising collecting signal samples from the wireless device by one or more LMUs and detecting a TOA from the signal samples by segmenting the collected signal samples to a predetermined length, determining an ambiguity function or correlation for each segment, and adding the ambiguity functions or correlations to detect a TOA. An estimated location of the wireless device may be determined as a function of the TOA.
Another embodiment of the present subject matter may provide a method for estimating a location of a wireless device comprising collecting signal samples from the wireless device by one or more LMUs and detecting a TOA from the signal samples by determining a mixing product of the collected signal samples, decimating the mixing product, segmenting the decimated product to predetermined lengths, determining ambiguity functions for each segment, and adding the ambiguity functions to detect a TOA. An estimated location of the wireless device may be determined as a function of the TOA.
An additional embodiment of the present subject matter provides a method for estimating a location of a wireless device in a wireless communication system having a plurality of nodes and a plurality of LMUs. The method may comprise collecting signal samples from the wireless device by one or more LMUs, detecting a TOA from the signal samples, and determining an estimated location of the wireless device as a function of the TOA where the TOA is detected without regard to noise and gain variation in the collected signal samples.
A further embodiment of the present subject matter provides a method for estimating a location of a wireless device in a wireless communication system having a plurality of nodes and a plurality of LMUs. The method may comprise collecting a set of signal samples from a first wireless device and a second wireless device by one or more LMUs in a search window determined as a function of a first uplink TOA from a first node. A second uplink TOA may be detected at a second node or LMU from the set of signal samples by a plurality of non-coherent additions of ambiguity functions. A range estimate of the wireless device may be determined, and an estimated location of the wireless device determined as a function of the first uplink TOA, the second uplink TOA, or the range estimate and second TOA.
These embodiments and many other objects and advantages thereof will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the embodiments.